This invention relates to xerography and, more specifically, to a novel photoreceptor member.
The art of xerography involves the use of a photosensitive element or member containing a photoconductive insulating layer which is first uniformly electrostatically charged in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation, such as light, X-ray or the like, which selectively dissipates the charge in the exposed areas of the photoconductive insulator by leaving behind a latent electrostatic image in the non-exposed areas. This latent electrostatic image may then be developed and then made visible by depositing finely divided electroscopic marking particles on the surface of the photoconductive layer. This concept was originally developed by Carlson in U.S. Pat. No. 2,297,691, and is further amplified and described by many related patents in the field.
One type of photoconductive layer used in xerography is illustrated by U.S. Pat. No. 3,121,006 to Middleton et al, which describes a number of binder layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic binder. In one commerical form, the binder layer contains particles of photoconductive zinc oxide dispersed in an insulating resin binder which is coated on a paper backing. In the Middleton et al patent, a relatively high volume concentration of photoconductor, up to about 50 percent or more by volume, is usually necessary in order to obtain sufficient photoconductor particle-to-particle contact for rapid discharge. Such high loadings of photoconductor in a binder layer, result in the physical continuity of the resin being destroyed, thereby significantly reducing the mechanical properties of the binder layer. In addition, the utilization of high photoconductor volume loadings, and correspondingly low binder concentrations, results in poor mechanical properties in terms of cohesion, adhesion, flexibility, toughness and/or results in a porous film which can result in undesirable humidity, sensitive and fatigue effects. At the same time surface porosity tends to negate residual toner removal and, therefore, the capability of repeated cycling of the photoreceptor in the xerographic imaging mode.
In U.S. Pat. No. 3,787,208, to R. N. Jones, the above high photoconductor concentration disadvantages were overcome by the discovery of a method of making a novel photoconductive binder layer which enables the use of relatively low photoconductor volume concentrations. In addition to excellent mechanical properties of such a binder layer, this binder layer also exhibits excellent electrical characteristics which enable the photoreceptor to be used in a cycling manner. The photoreceptor of the present invention further improves the electrical properties of the photoreceptor disclosed in Jones, U.S. Pat. No. 3,787,208 and in particular, improves long-term cyclic stability, increases spectral response and possesses positive charge capabilities over those exhibited by the photoreceptors disclosed in U.S. Pat. No. 3,787,208.